Response of predatory snails to a novel prey following the geographic range expansion of an intertidal barnacle

During a geographic range expansion, the success of a species colonizing a new region may be influenced by how resident predators respond to this novel prey. The volcano barnacle Tetraclita rubescens has recently expanded its range > 300 km northward along the coast of California, USA. In the historic portion of its range, Tetraclita is preyed upon by a southern dogwhelk, Nucella emarginata. In newly colonized northern habitats, Tetraclita has joined an assemblage of mid-intertidal barnacles preyed upon by two species of northern dogwhelks (N. ostrina and N. canaliculata). Using a combination of field enclosures and laboratory experiments, we tested the impacts of northern whelks on volcano barnacles relative to other barnacle species. In the field, juvenile Tetraclita were rarely consumed. In laboratory trials with larger barnacles, Tetraclita were nearly immune to drilling by northern whelks, perhaps due to superior morphological defenses. In all experiments, prior encounters with Tetraclita did not appear to increase the frequency of predation on this barnacle; northern whelk species rarely preyed on Tetraclita even when collected from a site where this barnacle was abundant. In contrast, the southern whelk N. emarginata readily preyed on Tetraclita in laboratory trials, perhaps reflecting a longer shared evolutionary history between these species. Overall, our results suggest that the success of a population established beyond a species' historical range boundary may be influenced by the functional traits of that species in relation to the composition and evolutionary history of the surrounding community.